The present invention pertains to wheelchairs for human travel and methods of manual propulsion of such wheelchairs. In particular, the present invention is a propulsive device and wheelchair including a mechanism with a continuous reciprocating linear or elliptical input path.
A large number and portion of the population in the U.S. use wheelchairs to cope with mobility impairments. The limitations imposed on these persons as a result of their reliance on wheelchairs significantly reduces their quality of life. In addition, many wheelchair users experience musculoskeletal injuries of the shoulder, elbow and wrist. These injuries are caused by the high force exertions, repetitive motions and awkward postures inherent in use of standard wheelchairs. In addition, the basic propulsive mode with a conventional wheelchair is one of asymmetric muscle use (push mode) leading to unbalanced muscle development. These problems may be complicated by limited upper extremity dexterity of those wheelchair users having spinal cord injuries. Fifty to 70 percent of wheelchair users experience some sort of shoulder pain, rotator tear, or impingement problem that can permanently hinder mobility and increase medical costs. The incidence of carpal tunnel syndrome among wheelchair users has been reported to be as high as 63 percent and research indicates that this may be a result of nerve compression from forceful exertions of the hand and wrist during wheelchair operation. Repetitive strikes of the heel of the hand against the wheel rim of conventional wheelchairs may cause pain and numbness of the thumb and fingers. The interaction of the user's body and their wheelchair is a direct consequence of the basic design of the conventional wheelchair and the associated necessary mode of propulsion.
The design of the typical manual wheelchair has endured, largely unchanged, due to its simplicity. Relatively recently, advances to wheelchair design have addressed the need for improved propulsive mechanisms. Various wheel cranks, geared hubs and the like have been proposed in the prior art to reduce the necessary force for propulsion. However, these prior art devices do not effectively allow for altering the user's posture nor modify the basic propulsive motion itself the primary factors contributing to injury. What is needed is a mechanism for propelling a wheelchair which allows for increased use of large muscle groups in symmetric operation, improved posture and reduced contact pressure to the user.